(emacs)Basic Window

Concepts of Emacs Windows
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When multiple windows are being displayed, each window has an Emacs
buffer designated for display in it. The same buffer may appear in more
than one window; if it does, any changes in its text are displayed in
all the windows where it appears. But the windows showing the same
buffer can show different parts of it, because each window has its own
value of point.
At any time, one of the windows is the "selected window"; the buffer
this window is displaying is the current buffer. The terminal's cursor
shows the location of point in this window. Each other window has a
location of point as well, but since the terminal has only one cursor
there is no way to show where those locations are. When you make
multiple frames, each frame has a cursor which appears in the frame's
selected window.
Commands to move point affect the value of point for the selected
Emacs window only. They do not change the value of point in any other
Emacs window, even one showing the same buffer. The same is true for
commands such as `C-x b' to change the selected buffer in the selected
window; they do not affect other windows at all. However, there are
other commands such as `C-x 4 b' that select a different window and
switch buffers in it. Also, all commands that display information in a
window, including (for example) `C-h f' (`describe-function') and `C-x
C-b' (`list-buffers'), work by switching buffers in a nonselected window
without affecting the selected window.
When multiple windows show the same buffer, they can have different
regions, because they can have different values of point. This means
that in Transient Mark mode, each window highlights a different part of
the buffer. The part that is highlighted in the selected window is the
region that editing commands use.
Each window has its own mode line, which displays the buffer name,
modification status and major and minor modes of the buffer that is
displayed in the window. Note:Mode Line, for full details on the
mode line.